1. Field of the Invention
The present invention relates to small internal combustion engines of the type used with lawnmowers, lawn tractors, other utility implements, and in sport vehicles, for example. In particular, the present invention relates to a passive secondary air muffler for such engines.
2. Description of the Related Art
Small internal combustion engines of the type used with lawnmowers, lawn tractors, other small utility implements, or in sport vehicles typically include an intake system including a carburetor attached to the engine which mixes liquid fuel with atmospheric air to form a fuel/air mixture which is drawn into the engine for combustion. In some air-cooled small engines, a relatively rich combustion mixture may be provided to ensure adequate performance while preventing the engine from overheating. Combustion of the fuel/air mixture produces exhaust emissions which leave the engine via an exhaust port, to which a muffler is attached.
One way to reduce the exhaust emissions of an internal combustion engine is to use a catalytic converter to treat the exhaust emissions of the engine. For small internal combustion engines, it is often desirable to combine the catalytic converter with a muffler into a single, compact unit. In such mufflers, if is often necessary to introduce auxiliary or secondary air from the atmosphere into the exhaust gas stream upstream of the catalytic converter to provide oxygen for conversion of residual hydrocarbons in the catalytic converter.
What is needed is a secondary air muffler which improves the efficiency of the catalytic converter and is inexpensive to manufacture.